The present invention relates to the field of well completion assemblies for use in a wellbore. More particularly, the invention provides a method and apparatus for completing and producing from multiple mineral production zones, independently or in any combination.
The need to drain multiple-zone reservoirs with marginal economics using a single well bore has driven new downhole tool technology. While many reservoirs have excellent production potential, they cannot support the economic burden of an expensive deepwater infrastructure. Operators needed to drill, complete and tieback subsea completions to central production facilities and remotely monitor, produce and manage the drainage of multiple horizons. This requires rig mobilization (with its associated costs running into millions of dollars) to shut off or prepare to produce additional zones from the central production facility.
Another problem with existing technology is its inability to complete two or more zones in a single well while addressing fluid loss control to the upper zone when running the well completion hardware. In the past, expensive and often undependable chemical fluid loss pills were spotted to control fluid losses into the reservoir after perforating and/or sand control treatments. A concern with this method when completing upper zones is the inability to effectively remove these pills, negatively affecting the formation and production potential and reducing production efficiency. Still another problem is economically completing and producing from different production zones at different stages in a process, and in differing combinations. The existing technology dictates an inflexible order of process steps for completion and production.
Prior systems required the use of a service string, wire line, coil tubing, or other implement to control the configuration of isolation valves. Utilization of such systems involves positioning of tools down-hole. Certain disadvantages have been identified with the systems of the prior art. For example, prior conventional isolation systems have had to be installed after the gravel pack, thus requiring greater time and extra trips to install the isolation assemblies. Also, prior systems have involved the use of fluid loss control pills after gravel pack installation, and have required the use of through-tubing perforation or mechanical opening of a wire-line sliding sleeve to access alternate or primary producing zones. In addition, the installation of prior systems within the wellbore require more time consuming methods with less flexibility and reliability than a system which is installed at the surface. Each trip into the wellbore adds additional expense to the well owner and increases the possibility that tools may become lost in the wellbore requiring still further operations for their retrieval.
While pressure actuated valves have been used in certain situations, disadvantages have been identified with such devices. For example, prior pressure actuated valves had only a closed position and an open position. Thus, systems could not reliably use more than one such valve, since the pressure differential utilized to shift the first valve from the closed position to the open would be lost once the first valve was opened. Therefore, there could be no assurance all valves in a system would open.
There has therefore remained a need for an isolation system for well control purposes and for wellbore fluid loss control, which combines simplicity, reliability, safety and economy, while also affording flexibility in use.